In a civil engineering work site or a quarry site of a mine, various working vehicles such as a dump truck and an excavator are operated. Particularly, a superjumbo working vehicle is used in a mine. Since such a working vehicle has a vehicle width, a vehicle height, and a longitudinal length noticeably larger than those of a general vehicle, it is difficult for an operator to check and understand a peripheral circumstance by a side mirror and the like. For this reason, there is proposed a device which monitors a periphery of a vehicle as a technique for assisting a running operation by helping the operator to simply recognize a vehicle periphery environment. For example, there is disclosed a technique in which a graphic image or an outline image showing the entire dump truck at the bird's eye position transparently overlaps bird's eye images based on outputs of a plurality of cameras (see Patent Literature 1).